Why don't you use the CGI solution? With suitable parameters, you can have a very generic image generator with that.

As for your problem, try this:

open (TEST,">$image_test") || die;
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See? There is a ">" in front of the filename.

And lastly, you will want to get a copy of Programming Web Graphics with Perl and Gnu Software.

Update: tilly reminded me that the die in the code I gave is "uninformative". Well, he is right, of course. You should use:

open(TEST,">$image_test") 
    || die "Error: no open (write mode) for '$image_test': $!";
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Christian Lemburg
Brainbench MVP for Perl
http://www.brainbench.com